At present, Freon-based refrigerants that have stable properties and are easy to be handled are used as refrigerants of an apparatus having a refrigeration cycle such as a refrigerator and an air conditioner.
However, although the Freon refrigerants have stable properties and are easy to be handled, it is said that the Freon refrigerants destroy the ozone layer, and since the Freon refrigerants adversely affect the global environment, the use of the Freon refrigerants will be entirely prohibited in the future after a preparatory period of time. Among the Freon refrigerants, hydro fluorocarbon (HFC) refrigerants do not seem to destroy the ozone layer, but they have properties to facilitate the global warming. Especially in Europe where the people are concerned about environmental problems, there is a tendency to prohibit the use of this refrigerant also. That is, there is a tendency that the use of the Freon refrigerants that are artificially produced is prohibited, and natural refrigerants such as hydrocarbon are used as in the past. However, such natural refrigerants are flammable, and limited resources must be used effectively, there is a problem that the amount of usage must be controlled.
Therefore, when refrigerant such as propane or isobutane is used in the apparatus having the refrigeration cycle, in order to reduce the amount of refrigerant to be used, it is effective to use refrigerating machine oil having less mutual solubility with the refrigerant.
However, in order to reduce the mutual solubility between the refrigerant and the refrigerating machine oil, since the polarity of the refrigerant is almost nonpolar, it is effective to use refrigerating machine oil having great polarity, but there is a problem that refrigerating machine oil having great polarity is liable to absorb water, and refrigerating machine oil which absorbs water is decomposed by strong sliding movement.
Thereupon, it is an object of the present invention to prevent the decomposition of refrigerating machine oil due to absorption of water, and to reduce the amount of refrigerant used in an apparatus having a refrigeration cycle by using refrigerating machine oil having less mutual solubility with the refrigerant.
Another object of the invention is to further reduce the amount of refrigerant used in the apparatus having the refrigeration cycle by using refrigerating machine oil suitable for reducing the refrigerant.
Another object of the invention is to provide an apparatus having a refrigeration cycle capable of obtaining the long term reliability by using refrigerating machine oil which generates few sediment and which is excellent in sealing performance and lubricating performance of sliding surface.